Pulmonary infections

Lung abscess

Diagnosis is based on a history of chronic cough and weight loss, with halitosis, clubbing, and the production of copious foul-smelling sputum. The CXR is usually diagnostic with an air-fluid level in the lung parenchyma. Air-fluid levels in the pleural space tend to be of different lengths on the PA and lateral CXR, and will be continguous with the chest wall. The two conditions may co-exist if the abscess ruptures into the pleural space.

Two important differential diagnoses to consider in a patient with an air-fluid level but otherwise atypical features for suppurative lung disease are ruptured hydatid cysts and (particularly for centrally positioned lesions) gastic herniation. Multiple air-fluid levels in one side of the chest, often the left, should raise concerns about diaphragmatic rupture with bowel in the chest cavity.

Management of lung abscess

Look for a cause – epilepsy, alcohol abuse, and dental caries. Accidental foreign body aspiration is less common in adults than children, but should be considered, especially if the abscess is slow to resolve or recurs. This is an indication for bronchoscopy. Explain to the patient on admission that therapy will be protracted.

• Regular postural drainage is an essential part of management.
• Penicillin 2 MU IVI 6 hourly and metronidazole 400 mg 8 hourly orally is traditional, but oddly enough no cheaper than amoxicillin-clavulanate 1.2 g IV 8 hourly, which is probably the agent of choice now. (Don’t need the metronidazole if use this.)
• Duration of therapy is classically 4 to 6 weeks, but many clinicians are comfortable with changing to oral therapy as soon as the patient has been apyrexial for 24 to 48 hours: amoxicillin/clavulanate 875/15 mg 2x/d (drop the metronidazole.)
• Continue therapy until there is complete resolution both clinically and radiologically (i.e. no fluid level visible on the CXR.).
• In patients who are allergic to penicillin, use clindamycin 600 mg 3x/d IV followed by 300 mg 3x/d orally.
• Image-guided percutaneous drainage may be worth considering.¹

Bronchiectasis.

In the situation of obvious suppurative lung disease on CXR this diagnosis is easy. It is important, however, not to miss the diagnosis in the individual who only has a suggestive history. Coarse crackles, even in the absence of CXR abnormalities, should alert one to the diagnosis in the presence of an appropriate history. Be aware that chronic lung disease of this nature exists, and that not all old thin, sick people have tuberculosis – the management of the two conditions is very different.

• Treat with ceftriaxone 1 g daily (2 g daily in areas with higher pneumococcal MICs). Once the patient is apyrexial for 24 hours, or in patients with milder disease, use amoxyclav 1 g 2x/d orally. If Psuedomonas is grown on culture (and the patient is not already recovered by the time the result is available) add ciprofloxacin 750 mg orally 2x/d.
• Treat associated bronchospasm if present.
• Ensure that physiotherapy is started early, and make sure the patient is taught the principles of postural drainage at home.
• Beware of the finding of an isolated microbial oddity on sputum culture – it is unlikely that it will be the only pathogen. However the finding of pseudomonas or klebsiella species on two specimens in a patient who is not settling should lead to consideration of a treatment regimen change to include a fluoroquinolone and perhaps a second agent such as an aminoglycoside.
• Remember to continue treatment for long enough – at least two weeks.

When discharging home, give out a patient held card explaining the diagnosis and the need to treat exacerbations promptly at the local health facility.

Community acquired pneumonias

The published aetiologies of community acquired pneumonias vary between countries (e.g. pneumococcus accounting for 45% in Kenya, 48% in the UK, 22% in Thailand, and only 13% in the USA. Mycoplasma and Chlamydia, on the other hand, accounted for 41% of USA cases, 21% in Thailand, 16% in the UK, and only 3% in Kenya.)² Hence guidelines need to be tailored to look at the local prevalence patterns.

Assessing severity of pneumonia

Recommendations about ‘poorer prognosis’ patients ³ who should all be admitted should be treated with caution – just because your patient doesn’t fulfil these criteria does not mean that admission is inappropriate. Remember that even for local patients, transport back to the hospital in the middle of the night is often difficult. Patients you could consider sending home are young, have a clear cut lobar pneumonia, have been sick for more than a day, aren’t tachypnoeic on room air, and are happy not to be admitted. Remember that tuberculosis can present with an apparently acute illness.

Perspective – severity assessment.

The various scoring systems, e.g. PSI,⁴ BTS, and modified BTS⁵ , are either quite difficult to use (PSI) or only modestly sensitive and specific (mBTS). A further modification⁶ is potentially of more use:

CURB-65 criteria: One point for each of

• Confusion
• Urea > 7 mmol/l
• Resp rate > 30/min
• Blood pressure systolic <90, or diastolic < 60
• Age > 65 years

Mortality was less than 1% when no features are present, was 3% if there were one or two features, and rose to 17% if there were 3 features. The presence of 4 features had a specificity of 93% (LR+ 2.7) for mortality, and this number was particular concerning as it was associated with a mortality rate of 42%.

Diagnostic pointers

Guesses about the aetiology of a chest infection at the time of presentation are just that – guesses. Having access to the CXR often doesn’t help much.

Therapy – CAP

Ceftriaxone 1 g daily IV is reasonable except in areas where the MIC for pneumococci is rising, in which case increase the daily dose to 2 g. It is not necessary to dose ceftriaxone 12 hourly for this condition. Once the temperature has settled, change to oral amoxycillin. De-escalation is relatively safe after 4 days (in the face of a negative blood culture in many studies, however), but still not practiced well.⁷.

For the elderly (>65 years), those with underlying illnesses (e.g. diabetes, renal failure, HIV), or those with more severe disease (confusion, low sats or low BP, or with respiratory rate of more than 30) use ceftriaxone 1g daily IV and azithromycin 500mg PO daily.

If allergic to penicillin and cephalosporins consider moxifloxacin 400 mg/d PO.

Although most guidelines recommend blood culture on admission, there is little evidence that this strategy beneficially influences subsequent management.⁸ Blood cultures are not cheap – reserve their use for the very ill or for those in whom you ‘guess’ that there may be an unusual organism.

Hospital acquired pneumonia

HAP is recognised as a pneumonia developing within 48 hours of admission which was not present on admission. Specifically, a patient with probable active PTB who has failed to respond to ceftriaxone after two days in the ward does not have a HAP.

Management is very similar to infections acquired in the community, except that there is a need to cover more broadly for gram-negative infections specifically Pseudomonas, Klebsiella, E coli, and Acinetobacter.

Treatment 

Depending on setting and likely exposure to cephalosporins, ceftriaxone 2g daily IV plus amikacin 15 mg/kg daily IV (i.e. for a 70 kg person amikacin 1 g/d) used to be a reasonable start, but as out of hospital cephalosporin use has now increased dramatically still use the amikacin, but instead of ceftriaxone consider piperacillin-tazobactam 4.5 g 8 hourly IV.

i.e.:

• piperacillin-tazobactam 4.5 g 8 hourly IV PLUS
• amikacin 15 mg/kg IV daily

In consultation with a specialist, it may be reasonable to use a carbapenem with activity against Pseudomonas (i.e. not ertapenem). The options are imipenem 1g 8 hourly IV (but because of poor CNS penetration and potenial to worsen seizures, don’t use this agent if a CNS infection is also suspected, or if the patient has epilepsy) or (if CNS cover is needed as well) meropenem 2 g 8 hourly IV. These agents are often highly effective, very pricey, can lead to the development of highly resistant infections, and should always be used with very careful thought, and not just because an organisms has grown on a culture with an “S” for sensitive next to the antibiotic’s name.

Aspiration pneumonia

Aspiration is common, and it is important to think of this condition. Not all aspiration events require an antibiotic – a chemical pneumonitis is well described.

However, in a patient with fever and leukocytosis, most clinicians would be keen to treat. Use either ceftriaxone and metronidazole or amoxicillin-clavulate 1.2 g 8 hourly, followed by oral treaatment once stable and afebrile for at least 24 hours.

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1. Lee JH, Hong H, Tamburrini M, Park CM. Percutaneous transthoracic catheter drainage for lung abscess: a systematic review and meta-analysis. Eur Radiol. 2022 Feb;32(2):1184-1194. doi: 10.1007/s00330-021-08149-5. Epub 2021 Jul 29. PMID: 34327579. ↩

2. File TM. Community-acquired pneumonia. Lancet. 2003;362:1991-2001 ↩

3. Bartlett JG, Mundy LM. Community-acquired pneumonia. N Engl J Med. 1995;333:1618-1623 ↩

4. Fine MH, Auble TE, Yealy DM, et al. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med. 1997;336:243-50 ↩

5. Neill AM, Martin IR, Weir R, et al. Community acquired pneumonia: aetiology and usefulness of severity criteria on admission. Thorax. 1996;51:1010-6 ↩

6. Lim WS, van der Eerden MM, Laing R, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003;58:377-82 ↩

7. Abhishek Deshpande, Sandra S Richter, Sarah Haessler, et al. De-escalation of Empiric Antibiotics Following Negative Cultures in Hospitalized Patients With Pneumonia: Rates and Outcomes, Clinical Infectious Diseases, 2021;72:1314–1322  ↩

8. Glerant JC, Hellmuth D, Schmit JL, et al. Utility of blood cultures in community-acquired pneumonia requiring hospitalisation: influence of antibiotic treatment before admission. Resp Med. 1999:93:208-212 ↩

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